Acute, Sublethal Cyanide Poisoning in Mice Is Ameliorated by Nitrite Alone: Complications Arising from Concomitant Administration of Nitrite and Thiosulfate as an Antidotal Combination

Abstract

Sodium nitrite alone is shown to ameliorate sub-lethal cyanide toxicity in mice when given from ~1 hour before until 20 minutes after the toxic dose as demonstrated by the recovery of righting ability. An optimum dose (12 mg/kg) was determined to significantly relieve cyanide toxicity (5.0 mg/kg) when administered to mice intraperitoneally. Nitrite so administered was shown to rapidly produce NO in the bloodsteam as judged by the dose dependent appearance of EPR signals attributable to nitrosylhemoglobin and methemoglobin. It is argued that antagonism of cyanide inhibition of cytochrome c oxidase by NO is the crucial antidotal activity rather than the methemoglobin-forming action of nitrite. Concomitant addition of sodium thiosulfate to nitrite-treated blood resulted in the detection of sulfidomethemoblobin by EPR spectroscopy. Sulfide is a product of thiosulfate hydrolysis and, like cyanide, is known to be a potent inhibitor of cytochrome c oxidase; the effects of the two inhibitors being essentially additive under standard assay conditions, rather than dominated by either one. The findings afford a plausible explanation for an observed detrimental effect in mice associated with the use of the standard nitrite-thiosulfate combination therapy at sub-lethal levels of cyanide intoxication.

Metalloporphyrin CoIIITMPyP Ameliorates Acute, Sublethal Cyanide Toxicity in Mice

“…We attempted a few experiments in which the Co III TMPyP was given 2 min following the cyanide, obtaining righting recovery times that were comparable to controls, but less reproducible (not shown) and these were not continued to statistical significance. In contrast, in a previous study 6 we showed that sodium nitrite was markedly antidotal if given 2 min after the cyanide (reproduced as the last column in Figure 6). Collateral deaths in these experiments occurred between 1.5 and 3 min and behavioral indications of toxicity were already apparent 1 min after injection of the cyanide, suggesting the toxic dose to have become systemically distributed by 1 min onwards.…”

“…We interpret the more rapid action of sodium nitrite to be a consequence of its ability to directly protect cytochrome c oxidase from inhibition within the mitochondrion. 6 Scavengers like Co III TMPyP must work more passively by binding available cyanide in the circulating bloodstream, or as may have been the case to some extent in the present experiments, any remaining within the intraperitoneal cavity.…”

“…It is becoming increasingly difficult to obtain IACUC approval for protocols where death is the endpoint. To combat this problem, Crankshaw et al 7 developed a procedure that we have slightly modified Cambal et al 6 in which amelioration of cyanide toxicity may be assessed sub-lethally in mice. Intraperitoneal (i.p.)…”

“…sodium pentobarbital followed by cervical dislocation. Righting recovery times were assessed based on the method of Crankshaw et al 7 with minor changes as described by Cambal et al 6 . Following injections, mice were placed in clear plastic tubes in a supine position.…”

“…The administration of toxin (time = 0 min, n=6, designated control) was followed by the administration of antidote at the following times and doses: 68 mg/kg Co III TMPyP (at t = 1 min, n = 4); 10 mg/kg NaNO 2 (at t = 1 min, n = 5); or 4-16 mg/kg NaNO 2 (at t = 2 min, n > 80 6 ); all i.p. The surviving mice were then placed on their backs and the times at which the animals righted were recorded (see Methods).…”